1. Field of the Invention
The present invention relates to an apparatus and method for maximizing or extending the longevity of arc tube bulbs. Specifically, the present invention relates to a method for preheating a high-intensity discharge light bulb to extend the life of the bulb, to reduce the power draw during pulsing operation, as well as to get full light intensity when pulsing begins.
2. Background of the Invention and Related Art
Arc tubes, like those found in high-intensity discharge lamps, have a variety of applications including emergency vehicles, automobile headlights, outer-space applications, and airplane landing/taxi lights. High-intensity discharge lamps or HIDs are particularly adapted to these applications because of the high luminescence that they produce. This brightness can be helpful in both alerting others of the user's presence, as well as illuminating a desired location.
The present invention is particularly useful as a means to alert others to the presence of certain activities or vehicles. Many applications benefit from the HID bulbs being able to pulse on and off or from an un-energized to an energized state and cycling the illumination. Lighting a cold arc tube in an HID lamp consumes enormous amounts of energy and requires high voltage. This high voltage requirement and power consumption continue for an extended period of time when operating in pulse mode because the HID lamp, when it is initiated in pulse mode, spends as much time off as it does on, permitting repeated cooling of the tube. Thus, the time required to reach an efficient, steady state operating temperature is significantly increased. The repeated ramping up and dropping off voltage to light the arc tube, i.e., in a cooler than operating steady state, accelerates the wear and deterioration of the electrodes, thus slowly increasing the distance or gap between the electrodes. This problem of increasing distance between the electrodes further increases the amount of voltage required to spark the arc tube and generate light. Thus, it can be seen that operating an HID in a pulsing mode, as taught by the prior art, reduces the longevity of the bulb or electrodes and ballast circuitry, thus requiring frequent replacement of the bulbs and/or ballast circuitry.
Frequent striking the arc tube in a cooler state also places an increased amount of stress on the ballast or circuitry used to strike the bulb arc. As discussed above, operating a cold or warm arc tube requires substantially more wattage than operating a hot bulb or a bulb at operating steady state. Thus, when a cold or warm bulb is initiated in a pulsing mode directly, it places stress on circuitry and requires sustained high-power draws until the bulb reaches a steady state operating temperature.
Finally, when a bulb goes from a cold temperature or off mode directly to a pulsing mode, the full brightness of the bulb is not realized because the metal halide salts in the arc tube are not sufficiently vaporized to a plasma state. It is only after an extended duration of operation in pulsing mode that the lights can attain full brightness, due to the slowed warm up phase.